1. Field of the Invention
The present invention relates to a webbing retractor which can impede pulling-out of a webbing at a time when a vehicle rapidly decelerates or the like, and in particular, to a webbing retractor which, after impeding pulling-out of a webbing, enables the webbing to be pulled out again.
2. Description of the Related Art
Generally, in a webbing retractor, a webbing is wound in a roll form on a hollow cylindrical spool supported at a frame which is formed in a substantial U-shape as seen in plan view and which is fixed to a vehicle. Usually, the webbing can be freely taken-up or pulled-out due to the spool rotating freely. Further, in the webbing retractor, a WSIR (webbing sensitive inertia reel) or a VSIR (vehicle sensitive inertia reel) is utilized in order to impede pulling-out of the webbing when a rapid deceleration of the vehicle or a rapid pulling-out of the webbing is sensed.
Hereinafter, a conventional webbing retractor equipped with a WSIR and a VSIR will be described on the basis of FIGS. 10A and 10B.
In FIGS. 10A and 10B, a webbing retractor 100 is shown in a side view seen from a rotational axis direction of a spool 102. The webbing retractor 100 is formed to include the spool 102; a lock plate 104 which is supported at the spool 102 so as to be freely swingable and which can mesh with ratchet teeth 106 provided at a frame (not shown); a V gear 108 which is provided coaxially with the spool 102, and when relative rotation with respect to the spool 102 arises, the V gear 108 guides the lock plate 104 to a position at which engagement with the ratchet teeth 106 is possible; a W sensor portion 110 which forms the WSIR; and a V sensor portion 120 which forms the VSIR.
In this webbing retractor 100, usually, the spool 102 and the V gear 108 rotate integrally. Thus, the webbing can be freely taken-up and pulled-out (the state shown in FIG. 10A) without the lock plate 104 engaging the ratchet teeth 106.
On the other hand, when the webbing is pulled-out rapidly, an inertia plate 116 of the W sensor portion 110 cannot follow the rotation of the V gear 108 (the spool 102) in the webbing pull-out direction (direction A in FIGS. 10A and 10B), and an inertial delay arises. As a result, relative rotation in the webbing take-up direction arises between the inertia plate 116 and the V gear 108. A pawl 112 which abuts the inertia plate 116 is swung in the webbing take-up direction and engages with internal teeth 118 fixed to the frame, and rotation of the V gear 108 in the webbing pull-out direction is impeded (the state shown in FIG. 10B).
Here, an engagement surface 118a of the internal tooth 118, which engagement surface 118a engages with the pawl 112, stands substantially perpendicular with respect to direction A. As a result, the tooth tip of the pawl 112 which engages with the engagement surface 118a is reliably guided to the tooth bottom of the internal tooth 118. A phase offset by which the pawl 112 is guided to the next internal tooth 118 and which is due to deficient engagement, and damage to the W sensor portion 110 accompanying such phase offset, are prevented.
When the rotation of the V gear 108 in the webbing pull-out direction is impeded, relative rotation is generated between the V gear 108 and the spool 102 which continues to rotate along with the pulling-out of the webbing. As a result, the lock plate 104, which has a guide pin 104a which is inserted into a guide hole 108a formed in the V gear 108, does not follow the rotation of the spool 102, and is guided by the guide hole 108a via the guide pin 104a, and reaches a position at which engagement with the ratchet tooth 106 is possible (a position at which the lock plate 104 and the tooth tip of the ratchet tooth 106 engage). The lock plate 104, which has been guided to the position at which engagement with the ratchet tooth 106 is possible, is guided to the tooth bottom of the ratchet tooth 106 by the configuration of the ratchet tooth 106, and is set in a locked state. In other words, the lock plate 104 is self-locked, and rotation of the spool 102 in the webbing pull-out direction is impeded.
At the time of this self-locking, the lock plate 104 moves toward the tooth bottom of the ratchet tooth 106 (i.e., toward the left in FIGS. 10A and 10B). Accompanying this movement of the lock plate 104, the guide pin 104a pushes the guide hole 108a side wall of the V gear 108 toward the left in FIG. 10, and due to this pushing moment, the V gear 108 rotates in the webbing take-up direction (direction B in FIGS. 10A and 10B). When the V gear 108 rotates by a predetermined amount in direction B, the engagement of the pawl 112 and the internal tooth 118 is cancelled. The pawl 112, which is urged to swing in direction A by being connected to one end of a spring 114 whose other end is fixed to the V gear 108, returns to its original position. In other words, the operation of the W sensor portion 110 is cancelled.
In this way, in the process in which the pulling-out of the webbing is impeded, operation of the W sensor portion 110 is cancelled. As a result, thereafter, pulling-out of the webbing is again possible.
In order to cancel the operation of the W sensor portion 110, a W sensor cancel angle xcex1 shown in FIG. 10B must be smaller than the angle of rotation in direction B of the V gear 108 (hereinafter called the V gear reverse rotation angle). The W sensor cancel angle xcex1 is an angle necessary for a peak portion C of the internal tooth 118, with which the pawl 112 is engaged, to move relatively with respect to the V gear 108 (the pawl 102) to an intersection point D of a swinging locus a of the tooth tip of the pawl 112 and a moving locus b of the peak portion of the internal tooth 118 (i.e., an angle necessary for the peak portion C to move relatively to a position at which no internal tooth 118 exists on the locus of swinging of the tooth tip of the pawl 112). Further, although not illustrated, after the V sensor portion 120 operates, even at the time when engagement of a sensor lever 122 and an external tooth 108b formed at the outer peripheral surface of the V gear 108 is released, the V sensor cancel angle must be smaller than the V gear reverse rotation angle.
However, at the conventional webbing retractor 100 such as described above, in order to prevent a phase offset at the time of operation of the W sensor portion 110, the engagement surface 118a of the internal tooth 118 must stand substantially perpendicular with respect to direction A, and the sensor cancel angle xcex1 cannot be made smaller by any more than a predetermined value. Further, there is dispersion in the dimensions of the internal teeth 118 within the predetermined range of dimensional accuracy, and due to this dispersion in dimensions, the values of the W sensor cancel angles xcex1 are not constant (the values of the W sensor cancel angles xcex1 vary depending on which internal tooth 118 the pawl 12 is engaged with). Further, the value of the W sensor cancel angle xcex1 also depends on the accuracy of assembly of the respective parts.
Thus, depending on the position of the internal tooth 118 with which the pawl 112 is engaged, there are cases in which the sensor cancel angle xcex1 is greater than the V gear reverse rotation angle and the operation of the W sensor portion 110 cannot be cancelled. Further, in order to make the maximum value of the W sensor cancel angle xcex1 always smaller than the V gear reverse rotation angle, excessive dimensional precision and assembly precision are required. Thus, a problem arises in that machinability and assemblability are poor, and costs increase. Further, there are of course similar problems with the V sensor portion 120 as well.
In view of the aforementioned, an object of the present invention is to provide a webbing retractor in which a webbing pull-out impeded state can be reliably cancelled without the need for excessive precision in the machining and assembly of parts, and in which, in predetermined cases, rotation of a spool in a webbing pull-out direction can be impeded without phase offset.
In order to achieve the above-described object, a webbing retractor of the present invention comprises: a spool which is tube-shaped and on which a webbing is taken-up and from which the webbing is pulled-out; a lock tooth formed at a surface, which intersects a rotation shaft of the spool, of a frame which is fixed and held at a vehicle and which rotatably supports both ends of the spool; a lock plate formed so as to be engageable with the lock tooth and connected to the spool so as to be freely swingable, and when the spool is rotated in a webbing pull-out direction from a position at which the lock plate can engage with the lock tooth, the lock plate is guided by the lock tooth and moved toward a tooth bottom of the lock tooth and engages with the lock tooth, such that the lock plate impedes rotation of the spool in the webbing pull-out direction; a lock wheel formed in a disc-shape and provided coaxially with the spool at one end side of the spool, the lock wheel usually rotating integrally with the spool and holding the lock plate at a position of non-engagement with the lock tooth, and when relative rotation arises between the lock wheel and the spool, the lock wheel guides the lock plate to a position at which engagement with the lock tooth is possible, and as the lock plate moves toward the tooth bottom of the lock tooth, the lock wheel is rotated in a webbing take-up direction; and a lock operation device having a pawl which is swingably supported and an engagement tooth which can engage with the pawl, the pawl usually being held at a position of non-engagement with the engagement tooth, and in a predetermined case, due to the pawl swinging and engaging with the engagement tooth, rotation of the lock wheel in the webbing pull-out direction is impeded, and due to the lock wheel being rotated in the webbing take-up direction, an engaged state of the pawl and the engagement tooth is cancelled, wherein an engagement surface of the engagement tooth, which engagement surface engages with the pawl, is formed in a circular arc shape corresponding to a locus of swinging of a region at which the pawl engages with the engagement tooth.
In the above-described webbing retractor, the spool, on which the webbing can be taken up and from which the webbing can be pulled-out, is supported so as to be freely rotatable. The lock plate is held by the lock wheel at a position of non-engagement with the lock tooth, and the pawl of the lock operation device is held at a position of non-engagement with the engagement tooth (the lock operation device is not operated). Thus, usually, the webbing can be freely taken-up and pulled-out.
In a predetermined case such as at the time the vehicle rapidly decelerates or at the time the webbing is rapidly pulled-out, when the lock operation device is operated, i.e., when the pawl engages with the engagement tooth, rotation of the lock wheel in the webbing pull-out direction is impeded. When rotation of the lock wheel in the webbing pull-out direction is impeded, relative rotation arises between the lock wheel and the spool from which the webbing is being pulled-out, and the lock plate is guided to a position at which engagement with the lock tooth provided at the frame is possible. As the spool rotates in the webbing pull-out direction, the lock plate, which is guided to the position where engagement with the lock tooth is possible, is guided by the lock tooth, and moves toward the tooth bottom of the lock tooth, and completely engages with the lock tooth (the lock plate and the lock tooth are self-locked). In this way, rotation of the spool in the webbing pull-out direction is impeded.
Further, at the time of the aforementioned self-locking, the lock wheel, which guides the lock plate to the position at which engagement with the lock tooth is possible, rotates in the webbing take-up direction as the lock plate moves toward the tooth bottom of the lock tooth. In this way, the engagement of the engagement tooth and the pawl of the lock operation device is cancelled (operation of the lock operation device is cancelled).
The engagement surface of the engagement tooth, which engagement surface engages with the pawl, is formed in a circular-arc shape in correspondence with the locus of swinging of the region at which the pawl engages with the engagement tooth (hereinafter, this region is called the pawl distal end). Therefore, when the lock operation device is operated, rotation of the lock wheel in the webbing pull-out direction is impeded without the pawl distal end being guided to the tooth bottom of the engagement tooth. Namely, regardless of what position of the engagement surface of the engagement tooth, which engagement surface engages with the pawl, the pawl distal end engages, the pawl is pushed and held at that engagement position. (For example, the pawl is pushed and held by the webbing tensile force which is slightly transmitted to the lock wheel via the rotation shaft of the spool or a spring for the lock wheel to maintain the lock plate at a position of non-engagement with the lock tooth at usual times.) Thus, rotation of the lock wheel in the webbing pull-out direction can be reliably impeded without a phase offset arising.
Further, the engagement surface of the engagement tooth, which engagement surface engages with the pawl, is formed in a circular-arc shape in correspondence with the locus of swinging of the pawl distal end. Thus, the angle needed for the operation of the lock operation device to be cancelled (hereinafter, the xe2x80x9csensor cancel anglexe2x80x9d) is a minimum value (substantially 0 [rad]). Namely, if the pawl and the engagement tooth are separated by an extremely small amount of an extent such that a pushing force, which is applied to the engagement portion of the pawl and the engagement tooth due to the webbing tensile force which is slightly transmitted to the lock wheel, is not applied to the pawl, the pawl can swing along the engagement surface of the engagement tooth which is formed in a circular-arc shape in correspondence with the locus of swinging of the pawl distal end. As a result, the pawl returns to its original position due to the force (e.g., the urging force of a spring) for maintaining the pawl at the position of non-engagement with the engagement tooth at ordinary times, and operation of the lock operation device is cancelled. In this way, a sufficiently small sensor cancel angle can be obtained by moderate machining precision and assembly precision of the engagement tooth. Thus, the operation of the lock operation device is reliably cancelled due to the rotation of the lock wheel in the webbing take-up direction, and after the pulling-out of the webbing is impeded, pulling-out of the webbing is again possible.
In this way, in the webbing retractor of the present invention, a webbing pull-out impeded state can be reliably cancelled without the need for excessive precision in the machining and assembly of parts, and, in predetermined cases, rotation of the spool in the webbing pull-out direction can be impeded without phase offset.
In the webbing retractor relating to the present invention, preferably, the engagement tooth of the lock operation device is formed at an inner peripheral surface of a tube-shaped member which is fixedly provided at the frame, and in a state in which the pawl of the lock operation device is accommodated within the tube-shaped member, the pawl is supported at the lock wheel so as to be freely swingable around a shaft which is parallel to the rotation shaft of the spool, and the pawl is connected to one end portion of an elastic body whose other end portion is connected to the lock wheel, and usually, the pawl is urged in a direction of non-engagement with the engagement tooth by urging force of the elastic body, and at a time when the webbing is rapidly pulled-out, the pawl swings in a direction of engaging with the engagement tooth against the urging force of the elastic body, and due to the lock wheel being rotated in the webbing take-up direction, the pawl separates from the engagement tooth and returns to a position of non-engagement with the engagement tooth due to the urging force of the elastic body.
In the webbing retractor of the present invention, it is preferable that, usually, the pawl is urged by urging force of an elastic body in a direction of non-engagement with the engagement tooth, and thus, the lock operation device does not operate.
When the webbing is pulled-out rapidly, the pawl, which is supported at the lock wheel, is swung in a direction of engaging with the engagement tooth (in the webbing take-up direction), relatively to the lock wheel, against the urging force of the elastic body. The pawl engages, without phase offset, with the engagement surface, which is formed in a circular-arc shape corresponding to the locus of swinging of the distal end of the pawl, of the engagement tooth which is formed at the inner surface of the tube-shaped member which is fixedly provided at the frame (i.e., the lock operation device is operated).
Further, when the lock wheel is rotated in the webbing take-up direction as the lock plate and the lock tooth self-lock, the pawl supported at the lock wheel separates from the engagement tooth, and, due to the urging force of the elastic body, returns to the position of non-engagement with the engagement tooth along the engagement surface which is formed in a circular-arc shape corresponding to the locus of swinging of the pawl distal end.
In this way, in the preferable webbing retractor of the present invention, a webbing pull-out impeded state can be reliably cancelled without the need for excessive precision in the machining and assembly of parts, and rotation of the spool in the webbing pull-out direction can be impeded without phase offset at the time when the webbing is rapidly pulled-out.
In the webbing retractor of the present invention, in the above-described webbing retractor, even more preferably, a region of engagement of the pawl with the engagement tooth is formed so as to correspond to a locus of swinging of the pawl.
In this webbing retractor, in the same way as the engagement surface of the engagement tooth, the engagement portion (pawl distal end) of the pawl, which engagement portion engages with the engagement tooth, corresponds to the locus of swinging of the pawl. Thus, in the state in which the pawl and the engagement tooth are engaged, there is planar contact, and rotation of the lock wheel in the webbing pull-out direction can be reliably impeded. Further, even if a portion of the pawl distal end and a portion of the engagement surface of the engagement tooth engage, rotation of the lock wheel in the webbing pull-out direction is impeded. For example, even at a position (swinging amplitude) at which engagement with the engagement tooth is impossible at a pawl whose distal end is acute, phase offset can be reliably prevented due to the pawl reliably engaging with the engagement tooth.
In this way, in the even more preferable webbing retractor, a webbing pull-out impeded state can be reliably cancelled without the need for excessive precision in the machining and assembly of parts, and, in predetermined cases, rotation of the spool in the webbing pull-out direction can be reliably impeded without phase offset.